Publications

Layered-to-Spinel Phase Transition in Li[sub x]MnO[sub 2]

Ab initio calculations suggest that partially lithiated layered transforms to spinel in a two-stage process. In the first stage, a significant fraction of the Mn and Li ions rapidly occupy tetrahedral sites, forming a metastable intermediate. The second stage involves a more difficult coordinated rearrangement of Mn and Li ions to form spinel. This behavior is contrasted to The susceptibility of Mn for migration into the Li layer is found to be controlled by oxidation state, which suggests various means of inhibiting the transformation. These strategies could prove useful in the creation of superior Mn-based cathode materials. © 2001 The Electrochemical Society. All rights reserved.

Experimental and Computational Evidence of Highly Active Fe Impurity Sites on the Surface of Oxidized Au for the Electrocatalytic Oxidation of Water in Basic Media

Abstract Addition of Fe to Ni‐ and Co‐based (oxy)hydroxides has been shown to enhance the activity of these materials for electrochemical oxygen evolution. Here we show that Fe cations bound to the surface of oxidized Au exhibit enhanced oxygen evolution reaction (OER) activity. We find that the OER activity increases with increasing surface concentration of Fe. Density functional theory analysis of the OER energetics reveals that oxygen evolution over Fe cations bound to a hydroxyl‐terminated oxidized Au (Fe–Au 2 O 3 ) occurs at an overpotential ∼0.3 V lower than over hydroxylated Au 2 O 3 (0.82 V). This finding agrees well with experimental observations and is a consequence of the more optimal binding energetics of OER reaction intermediates at Fe cations bound to the surface of Au 2 O 3 . These findings suggest that the enhanced OER activity reported recently upon low‐potential cycling of Au may be due to surface Fe impurities rather than to “superactive” Au III surfaquo species.

What is the Smallest Volume Into Which Light Can Be Focused, Efficiently?

Electromagnetic waves, running in close proximity to a metal surface, can have surprisingly short wave-lengths, as short as λ=1nm, at optical frequencies. Thus the phrase Optical frequencies but with X-ray wavelengths, is appropriate. In effect these plasmon waves can experience a high effective refractive index, n>>100, dependent on the exact guiding structure. We find moreover, that at these short wavelengths, the skin depth or exponential decay depth, inside the metal can be <1nm, much shorter than the conventional collisionless skin depth, c/ωp ~ 25nm in Silver. We propose an innovative dimple geometry as a focusing structure that makes it possible to focus visible frequencies down to ~5nm dimensions, with an efficiency of ~50%. This focusing structure is much more efficient, and leads to a much smaller spot size, than can be achieved with conventional pinhole structures. We introduce a new Figure-of-Merit for focusing that properly accounts for plasmonic energy dissipation. We find that the limit of focusing is reached when the electromagnetic plasmonic group velocity vg becomes as slow as the electron Fermi velocity, vF.

Substantial hysteresis in emergent temperature sensitivity of global wetland CH4 emissions

Oxydehydrogenation of ethane over ZSM-5 zeolite catalysts

Metabolic engineering of yeast for de novo production of kratom monoterpene indole alkaloids

CCDC 1822133: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Supernova 2000dg in MCG +1-1-29

Leaf and canopy energy budgets

The plant in a field of energy, or in any considered area in which gradients exist, reacts passively to its surroundings . . . it should be clear that the sun, or even outer space, is not more removed from the plant than the next millimeter of air; it is the specific part of heat exchange being considered that determines what should be included in the plant’s environment.Klaus Raschke (1960)

Resistance switching memories are memristors

All 2-terminal non-volatile memory devices based on resistance switching are memristors, regardless of the device material and physical operating mechanisms. They all exhibit a distinctive "fingerprint" characterized by a pinched hysteresis loop confined to the first and the third quadrants of the v–i plane whose contour shape in general changes with both the amplitude and frequency of any periodic "sine-wave-like" input voltage source, or current source. In particular, the pinched hysteresis loop shrinks and tends to a straight line as frequency increases. Though numerous examples of voltage vs. current pinched hysteresis loops have been published in many unrelated fields, such as biology, chemistry, physics, etc., and observed from many unrelated phenomena, such as gas discharge arcs, mercury lamps, power conversion devices, earthquake conductance variations, etc., we restrict our examples in this tutorial to solid-state and/or nano devices where copious examples of published pinched hysteresis loops abound. In particular, we sampled arbitrarily, one example from each year between the years 2000 and 2010, to demonstrate that the memristor is a device that does not depend on any particular material, or physical mechanism. For example, we have shown that spin-transfer magnetic tunnel junctions are examples of memristors. We have also demonstrated that both bipolar and unipolar resistance switching devices are memristors. The goal of this tutorial is to introduce some fundamental circuit-theoretic concepts and properties of the memristor that are relevant to the analysis and design of non-volatile nano memories where binary bits are stored as resistances manifested by the memristor's continuum of equilibrium states. Simple pedagogical examples will be used to illustrate, clarify, and demystify various misconceptions among the uninitiated.

Preparation and use of Leadfluor-1, a synthetic fluorophore for live-cell lead imaging

Inferring CO₂ fertilization effect based on global monitoring land-atmosphere exchange with a theoretical model

Abstract Rising atmospheric CO 2 concentration ([CO 2 ]) enhances photosynthesis and reduces transpiration at the leaf, ecosystem, and global scale via the CO 2 fertilization effect. The CO 2 fertilization effect is among the most important processes for predicting the terrestrial carbon budget and future climate, yet it has been elusive to quantify. For evaluating the CO 2 fertilization effect on land photosynthesis and transpiration, we developed a technique that isolated this effect from other confounding effects, such as changes in climate, using a noisy time series of observed land-atmosphere CO 2 and water vapor exchange. Here, we evaluate the magnitude of this effect from 2000 to 2014 globally based on constraint optimization of gross primary productivity (GPP) and evapotranspiration in a canopy photosynthesis model over 104 global eddy-covariance stations. We found a consistent increase of GPP (0.138 ± 0.007% ppm −1 ; percentile per rising ppm of [CO 2 ]) and a concomitant decrease in transpiration (−0.073% ± 0.006% ppm −1 ) due to rising [CO 2 ]. Enhanced GPP from CO 2 fertilization after the baseline year 2000 is, on average, 1.2% of global GPP, 12.4 g C m −2 yr −1 or 1.8 Pg C yr −1 at the years from 2001 to 2014. Our result demonstrates that the current increase in [CO 2 ] could potentially explain the recent land CO 2 sink at the global scale.

Corrosion in Supercritical Water Oxidation Systems: A Phenomenological Analysis

Pronounced corrosion damage occurs in supercritical water oxidation reactors, and few materials are immune to attack. In this paper, we describe a phenomenological model for the corrosion process, and we discuss the effect of electrolyte dissociation and water density, as influenced by temperature and pressure, upon the kinetics of corrosion of metals and alloys in supercritical water. The corrosion process at near‐critical temperatures is believed to involve acid attack, with the concentration of H+ being a function of the dissociation constant of , which is a major product of the oxidation of chlorinated organic waste, and of the density of the solution. We show that the competing effects of temperature on the heterogeneous rate constant and on the concentrations of H+ and leads to a pressure (and hence density)‐dependent maximum in the corrosion rate in the vicinity of the critical temperature. This result is in general agreement with experimental data on corrosion in aqueous solutions at near‐critical temperatures.

A High Depth Resolution Backside Secondary Ion Mass Spectrometry Technique Used for Studying Metal/Gaas Contacts

Extended Memristor Devices

4 Providing Flow Protection in SCORE

Faculty Opinions recommendation of Insights into antiamyloidogenic properties of the green tea extract (-)-epigallocatechin-3-gallate toward metal-associated amyloid-β species.

Read the full review for this Faculty Opinions recommended article: Insights into antiamyloidogenic properties of the green tea extract (-)-epigallocatechin-3-gallate toward metal-associated amyloid-β species.

Continental flood basalts drive Phanerozoic extinctions

Refinements of the geological timescale driven by the increasing precision and accuracy of radiometric dating have revealed an apparent correlation between large igneous provinces (LIPs) and intervals of Phanerozoic faunal turnover that has been much discussed at a qualitative level. However, the extent to which such correlations are likely to occur by chance has yet to be quantitatively tested, and other kill mechanisms have been suggested for many mass extinctions. Here, we show that the degree of temporal correlation between continental LIPs and faunal turnover in the Phanerozoic is unlikely to occur by chance, suggesting a causal relationship linking extinctions and continental flood basalts. The relationship is stronger for LIPs with higher estimated eruptive rates and for stage boundaries with higher extinction magnitudes. This suggests LIP magma degassing as a primary kill mechanism for mass extinctions and other intervals of faunal turnover, which may be related to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mrow><mml:msub><mml:mrow><mml:mrow><mml:mtext>CO</mml:mtext></mml:mrow></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mo>,</mml:mo><mml:mo> </mml:mo><mml:msub><mml:mrow><mml:mrow><mml:mtext>SO</mml:mtext></mml:mrow></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> , Cl, and F release. Our results suggest continental LIPs as a major, direct driver of extinctions throughout the Phanerozoic.